Analytic TDSBR Algorithm And Its Application In Electromagnetic Scattering Of Composite Targets

The research on the composite electromagnetic scattering problem of targets and backgrounds such as sea surface and sea targets has very important theoretical significance and practical application value for microwave remote sensing,target detection and identification and other fields.The analysis methods of electromagnetic scattering problem include theoretical research,experimental measurement and numerical simulation.Theoretical research can only give analytical solutions to a small number of targets,and experimental measurements are limited by various conditions such as being expensive or difficult to perform.Numerical simulation has great flexibility and is an important auxiliary method for the research of target characteristics.In the research of non-cooperative target electromagnetic properties,it is basically the main research method.Taking into account the actual situation,the compound target is generally a complex target with a super large size.Under normal circumstances,numerical algorithms such as Mo M,FEM and FDTD are difficult to meet the needs of practical problems.For composite targets with very large electrical dimensions,the use of high frequency approximations is a realistic approach.In this paper,the existing Time-Domain Shooting and Bouncing Ray(TDSBR)algorithm is improved by the analytic integration scheme,so that the scale of the integral region in the calculation is no longer dependent on the frequency of the electromagnetic wave.Using KD-Tree to speed up the intersection of ray and triangle facet,obviously improves the computational efficiency.Further,the parallel computation of TDSBR based on MPI is realized,and the composite electromagnetic scattering problem of super large electric target and background is calculated by using the super-computing Tianhe-2.The exploration of this paper is of fundamental significance to the development of autonomous and controllable high-frequency electromagnetic calculation software and support for the simulation of electromagnetic characteristics of complex environments in China.The details of the paper and the main research results are as follows:Firstly,the basic principle and implement method of TDSBR algorithm based on the analysis are introduced.Determining the virtual aperture surface according to thegeometric shape of target,and making the projection of the virtual aperture surface below the incident source point can completely block the target.Dividing the virtual aperture into a number of tubes and track all the propagation of the tube base on needs.Then,testing the intersection between the ray and the target to find the triangular face that intersects the ray and is closest to the ray source point.Afterwards,Calculating reflected rays and update the incident source point and direction of incidence until the rays do not intersect the target.Hereafter,recording the triangle element number and intersection point that intersected the ray for the last time,and then use the analytical time domain physical optics method to calculate the far field scattering field at the point of reception.Ultimately,the total scattered field of the target is obtained by superimposing the scattered fields calculated by all the ray tubes.For the initial ray tube that has no intersection with the target,it is treated as a null ray tube and is directly discarded.Secondly,the KD-Tree is used to accelerate the analytical TDSBR and significantly improves the computational efficiency.Although the analytical TDSBR can calculate the composite scattering of sea surface and super-large electric size targets,it still has a large amount of computational problems.KD-Tree mainly accelerates the process of the intersection of ray and triangular face.This paper uses Stack-KD stack traversal search algorithm and Rope-KD non-clustered trail traversal search algorithm to accelerate ray tracing process.Before the space acceleration of ray tracing,KD-Tree needs to be constructed,and the quality of KD-Tree directly affects the acceleration effect of these two KD-Tree search algorithms.For the Stack-KD algorithm,you need to create a stack.And for the Rope-KD,you need to add clues to the six faces of the node.Both of KD-Tree search algorithms are very obvious acceleration effect.Again,parallel computing based on MPI is implemented,which improves the computational efficiency and extends the application scope of the algorithm.This article designs the parallel implementation based on MPI.The ray tube is divided from the main process(0 process),and then the ray tube information is passed to other processes.According to the ray tubes are mutually independent,all the ray tube information is divided into each thread in parallel,all the threads simultaneously perform the intersection test of the ray and the target,including the KD-Tree algorithm acceleration process,and obtain each the far field scattering total field of allthe tubes in the thread at the receiving point.Finally,the total scattered field information calculated in each process is transmitted to the main process,and then the information is integrated and superimposed to obtain the target total scattered field.The MPI parallel technology greatly improves the computational efficiency of the TDSBR algorithm.The calculation of the national supernumerary Tianhe-2 actually shows that the algorithm has good compatibility and scalability.Finally,The proposed algorithm is applied to the analysis of electromagnetic scattering characteristics of composite targets.Calculate time-domain electromagnetic scattering characteristics of composite targets such as ground + target,sea + target,and sea + target above sea surface.